It has been heretofore known that the use of an organic silicon compound as a promotor component for a carried type Ziegler catalyst provides an improvement in the stereoregularity of the polymer thus produced.
Organic silicon compounds which have been heretofore proposed can be roughly divided into the following two groups:
(1) Dialkoxysilane compound (R.sub.2 Si(OMe).sub.2) (in which R represents an aromatic or aliphatic hydrocarbon group)
Examples of such dialkoxysilane compounds include diphenyldimethoxysilane compounds (as disclosed in JP-A-57-63310, 57-63311, 58-138708, 59-138708, 61-296006, 63-175008, 63-289004 (the term "JP-A" as used herein means an "unexamined published Japanese patent application")), diisobutyldimethoxysilane compounds (as disclosed in JP-A-62-18406, 63-258907, 2-70708, 2-173010, 3-33103), diisopropyldimethoxysilane compounds (as disclosed in JP-A-63-258907, 2-229807, 3-33102, 3-33103), dicyclopentyldimethoxysilane compounds (as disclosed in JP-A-2-229807), di-t-butyldimethoxysilane compounds (as disclosed in JP-A-2-70708, 2-229806, 3-33102), dicyclohexyldimethoxysilane compounds (as disclosed in JP-A-63-258907), t-butyl(t-butoxy)dimethoxysilane compounds (as disclosed in JP-A-3-119004), cyclohexylmethyldimethoxysilane compounds (as disclosed in JP-A-2-170803, 2-229807), cyclohexylethyldimethoxysilane compounds (as disclosed in JP-A-2-163104), and t-butylmethyldimethoxysilane compounds (as disclosed in JP-A-62-11705, 62-20507, 63-92615, 2-229807).
(2) Trialkoxysilane compound (RSi(OMe).sub.3) (in which R represents an aromatic or aliphatic hydrocarbon group)
Examples of such a trialkoxysilane compound include phenyltriethoxysilane compounds (as disclosed in JP-A-57-63311, 58-83006, 62-20507, 61-296006), ethyltriethoxysilane compounds (as disclosed in JP-A-57-63310), butyltriethoxysilane compounds (as disclosed in JP-A-2-170803), t-butyltrimethoxysilane compounds (as disclosed in JP-A-63-11705, 63-92615, 63-258907, 3-33106, 3-33105, 2-70708), isobutyltrimethoxysilane compounds (as disclosed in JP-A-3-33106), t-butyltriethoxysilane compounds (as disclosed in JP-A-2-229807), and norbornanetrimethoxysilane compounds (as disclosed in JP-A-63-92615).
However, the use of such a dialkoxysilane compound has some disadvantages. For example, a diphenyldimethoxysilane compound has a benzene ring on a silicon atom. When decomposed, such a diphenyldimethoxysilane compound releases the harmful benzene which is then left in the polymer thus produced, causing health problems.
On the other hand, diisopropyldimethoxysilane, dicyclopentyldimethoxysilane, dicylcohexyldimethoxysilane, di-t-butyldimethoxysilane, t-butyl(t-butoxy)dimethoxysilane, t-butylmethyldimethoxysilane compounds, etc. have an aliphatic hydrocarbon group as a substituent on a silicon atom and thus cause no health problems. However, all these compounds, which have a bulky substituent, can hardly be synthesized and thus are extremely expensive. Further, the polymer thus obtained leaves much to be desired in stereoregularity and melting point. Diisobutyldimethoxysilane, cyclohexylmethyldimethoxysilane, cyclohexylethyldimethoxysilane compounds, etc. can be synthesized by a hydroxylation reaction and thus are inexpensive. However, the polymer thus produced exhibits a low stereoregularity. Therefore, these compounds cannot be practical.
These organic silicon compounds are obtained by introducing a substituent onto a silicon atom in the presence of an organic metal compound such as Grignard reagent. Accordingly, trialkoxysilane compounds can be generally easily synthesized and inexpensively supplied on an industrial basis as compared with dialkoxysilane compounds. However, trialkoxysilane compounds which have heretofore been used (e.g., phenyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, t-butyltrimethoxysilane, isobutyltrimethoxysilane, t-butyltriethoxysilane, norbornanetrimethoxysilane) cause a remarkable drop in the catalyst activity and thus are economically disadvantageous and cannot be substantially put into industrial use. In order to inhibit the drop in the catalyst activity with such a trimethoxy compound, it has been recently proposed to use such a trimethoxy compound in combination with a dimethoxysilane compound as disclosed in JP-A-2-70708, 3-33103, 3-33105, and 3-33106. However, all these approaches involve the reduction in stereoregularity. These approaches are also disadvantageous in that a plurality of tanks for storing respective organic silicon compounds and from which these organic silicon compounds are supplied to production plants are needed.